Stench compound

Striped skunk (Mephitis mephitis) in a defensive posture with erect and puffed tail, indicating its readiness to spray

Stench compounds are chemicals, almost always organic chemicals, that have an unpleasant odor. Their odor contrasts with that of fragrance compounds.

Selected principles

Civetone, whose odor character depends on concentration: pleasant when dilute, unpleasant musty when concentrated

A stench can only be detected if the compound exhibits some volatility. As for fragrance compounds, volatility typically requires a molecular weight < 300.

An important factor relevant to stench is the odor detection threshold. Odors of compounds can also vary with concentration. Civetone, produced by civets, has a strong musky odor that becomes pleasant at extreme dilutions.[1]

Odor Thresholds for selected Compounds[2]
Compound name Compound type Threshold (ppm) Typical occurrence
5-Ethylidene-2-norbornene alkene 0.00014 synthetic
Trimethylamine amine 0.00003 spoiled fish
Isovaleric acid carboxylic acid 0.000078 vomit
tert-Butyl mercaptan thiol 0.0000029 Natural gas
Dimethylsulfide thioether 0.003 putrified flesh

Classes of stench compounds

Amines

Compound name Fragrance Natural occurrence Chemical structure
Trimethylamine Fishy
Ammonia 		Spoiled fish
Putrescine Rotting flesh Rotting flesh
Cadaverine Rotting flesh Rotting flesh
Pyridine Fishy Belladonna
Indole Fecal
Flowery 		Feces
Jasmine
Skatole Fecal
Flowery 		Feces
(diluted) Orange Blossoms

Sulfur compounds

Structure of E-2-butenethiol, a major component of skunk spray.

Sulfur is odorless, but many sulfur compounds have unpleasant odors. Prominent is hydrogen sulfide, which results from decaying proteins and is a major nuisance associated with the paper industry.[3] It is nonetheless an important signalling molecule in nature.[4] The vast inventory of organosulfur compounds typically have unpleasant odors. Thioacetone, a mixture of lightly studied organosulfur compounds is infamous for its strong stench.

A notable exception to the malodorous nature of thiols is grapefruit mercaptan, the odor of grapefruits. Furan-2-ylmethanethiol (aka furfuryl mercaptan, is the principal odor of roasted coffee.[5] Allyl thiol CH2=CHCH2SH) is a component of garlic breath.[6] (Methylthio)methanethiol (CH3SCH2SH) is found in male mouse urine and functions as a semiochemical for female mice. It has a strong garlic odor.[7]

The foul odors of thiols is exploited by skunks as components of their defensive spray. Gas chromatographic analysis of the spray from the spotted skunk (Spilogal putorius), revealed these three thiols: (E)-2-butene-1-thiol, 3-methyl-1-butanethiol, and 2-phenylethanethiol.[8][9]

Volatile organophosphorus and organoarsenic compounds characteristically have distinctive odors. Sometimes claimed as the first organometallic compound, Cadet's fuming liquid was reported in 1760 to smell like garlic.[10] It consisted mostly of dicacodyl (((CH3)2As)2) and cacodyl oxide (((CH3)2As)2O). The methylphosphines ((CH3)PH2, (CH3)2PH, and (CH3)3P have a garlic-metallic odors.[11]

Carboxylic acids

In contrast to the pleasant, often fruity odor of carboxylic acid esters, the parent carboxylic acids have unpleasant odors. Butyric acid is associated with spoiled dairy products. The C-5 acids, valeric acids are produced in the human gut.[12]

Safety and environment

Focusing on a prevalent stench compound, hydrogen sulfide is highly toxic. The risk of poisoning is made worse because it induces loss of olfactory perception at the ppm level.[13] With regards to remediation, hydrogen sulfide is readily trapped and destroyed by base and air. Similar treatment also applies to thiols.[3]

In the design of processes that have a potential to produce odor pollution, instruments and expert panels are employed to measure the intensity of odors. However, most instruments that measure concentration of air pollutants, whether via infrared analysis, colorimetry, adsorption, absorption, or surface tension, are limited in the compounds they can identify and have limited lower detection limits. For these reasons, human observation is often more reliable for evaluating odorous compounds. Stench compounds such as hydrogen sulfide are more readily detectable and are often given much lower acceptable concentrations in legal air quality standards, and counteraction is necessary to remove them from pollution streams to avoid irritation to the broader environment.[14]

References

  1. ^ Bedoukian, Paul Z. "Perfumery and Flavoring Synthetics", 2nd ed., p. 248, Elsevier, New York, 1967.
  2. ^ Imamura, Daichi; Akai, Motoaki; Watanabe, Shogo (2005). "Exploration of hydrogen odorants for fuel cell vehicles". Journal of Power Sources. 152: 226–232. Bibcode:2005JPS...152..226I. doi:10.1016/j.jpowsour.2005.01.007.
  3. ^ a b Pouliquen, Francois; Blanc, Claude; Arretz, Emmanuel; Labat, Ives; Tournier-Lasserve, Jacques; Ladousse, Alain; Nougayrede, Jean; Savin, Gérard; Ivaldi, Raoul; Nicolas, Monique; Fialaire, Jean; Millischer, René; Azema, Charles; Espagno, Lucien; Hemmer, Henri; Perrot, Jacques (2000). "Hydrogen Sulfide". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a13_467. ISBN 978-3-527-30385-4.
  4. ^ Zivanovic, Jasmina; Filipovic, Milos R. (2016). "Hydrogen sulfide: Stench from the past as a mediator of the future". The Biochemist. 38 (5): 12–17. doi:10.1042/bio03805012.
  5. ^ Panten, Johannes; Surburg, Horst (2015). "Flavors and Fragrances, 1. General Aspects". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–9. doi:10.1002/14356007.a11_141.pub2. ISBN 978-3-527-30673-2.
  6. ^ Block, E. (2010). Garlic and Other Alliums: The Lore and the Science. Royal Society of Chemistry. ISBN 978-0-85404-190-9.
  7. ^ Lin, D.Y.; Zhang, S.Z.; Block, E.; Katz, L.C. (2005). "Encoding social signals in the mouse main olfactory bulb". Nature. 434 (7032): 470–477. Bibcode:2005Natur.434..470L. doi:10.1038/nature03414. PMID 15724148. S2CID 162036.
  8. ^ Wood, William F.; Morgan, Christopher G.; Miller, Alison (1991). "Volatile components in defensive spray of the spotted skunk,Spilogale putorius". Journal of Chemical Ecology. 17 (7): 1415–1420. Bibcode:1991JCEco..17.1415W. doi:10.1007/bf00983773. PMID 24257801.
  9. ^ Wood, William F. (1999). "The History of Skunk Defensive Secretion Research". The Chemical Educator. 4 (2): 44–50. doi:10.1007/s00897990286a.
  10. ^ Seyferth, D. (2001). "Cadet's Fuming Arsenical Liquid and the Cacodyl Compounds of Bunsen". Organometallics. 20 (8): 1488–1498. doi:10.1021/om0101947.
  11. ^ Glindemann, D.; Dietrich, A.; Staerk, H.; Kuschk, P. (2005). "The Two Odors of Iron when Touched or Pickled: (Skin) Carbonyl Compounds and Organophosphines". Angewandte Chemie International Edition. 45 (42): 7006–7009. doi:10.1002/anie.200602100. PMID 17009284.
  12. ^ "Metabocard for Valeric acid". Human Metabolome Database. 2020-04-23. Retrieved 2020-09-30.
  13. ^ Fawcett, Howard H. (1948). "Hydrogen sulfide-killer that may not stink". Journal of Chemical Education. 25 (9): 511. doi:10.1021/ed025p511.
  14. ^ Bolz, Ray E. (2019-03-07). "Air Pollution and the Total Environment". CRC Handbook of Tables for Applied Engineering Science. CRC Press. pp. 731–737. ISBN 978-1-351-83842-9.
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